Control of infinitely variable transmission

ABSTRACT

A controller ( 80 ) calculates a target speed ratio of a continuously variable transmission ( 2 ) incorporated into an infinitely variable transmission for a vehicle and a target vehicle acceleration based on a vehicle running state. When a predetermined creep torque control condition holds (S 90 -S 93,  S 101 ), the controller ( 80 ) corrects the target speed ratio such that the deviation of the target acceleration from the real vehicle acceleration to decrease. By controlling the speed ratio of the continuously variable transmission to the corrected target speed ratio, the infinitely variable transmission generates a creep torque consistent with the driver&#39;s intention.

FIELD OF THE INVENTION

This invention relates to control of an infinitely variable transmissionof a vehicle.

BACKGROUND OF THE INVENTION

Tokkai 2000-179674 published by the Japanese Patent Office in 2000discloses an infinitely variable transmission (IVT) in which acontinuously variable transmission (CVT), a fixed speed ratiotransmission and a planetary gear set are combined.

The speed ratio of the IVT (IVT speed ratio) arbitrarily varies fromforward to reverse, including a geared neutral point (GNP) at which thespeed ratio becomes infinite, by changing the speed ratio of the CVT(CVT speed ratio).

At GNP, the output shaft of the IVT stops. In other words, only thevariation in the CVT speed ratio allows change-over between forward andreverse operation without using a forward/reverse change-over mechanism.

SUMMARY OF THE INVENTION

In this IVT, the CVT speed ratio is controlled based on the acceleratorpedal depression and vehicle speed. Even when the accelerator pedal isnot depressed, a small torque is transmitted to the drive wheels of thevehicle to cause the vehicle to creep, i.e., to make the vehicle move ata low speed. The creep torque transmitted to the drive wheels in thisstate is obtained through CVT speed ratio control wherein the CVT speedratio is feedback controlled so that the real vehicle speed detected bythe vehicle speed sensor coincides with the target vehicle creep speed.

As a result, when a driver depresses the brake pedal in order to stopthe vehicle at low speed, the difference between the real vehicle speedand the target vehicle creep speed increases and the CVT speed ratio iscontrolled to increase the creep torque transmitted to the drive wheelsin order to achieve the target vehicle creep speed.

This increase in the creep torque is opposite to the intention of thedriver who operates the brake to stop the vehicle, and the driver mayexperience an uncomfortable feeling.

Further, the design of the IVT results in the following output torquecharacteristics. When the CVT speed ratio corresponds to GNP, the torquetransmitted from IVT to the drive wheels is zero. When the CVT speedratio is slightly increased from the GNP, the output torque of the IVTundergoes a large and abrupt increase, and then it gradually decreasesas the CVT speed ratio further increases. Such an abrupt increase in theoutput torque of the IVT may adversely affect the smooth starting of thevehicle.

It is therefore an object of this invention to optimize the creep torqueof a vehicle equipped with an IVT through the speed ratio controlthereof.

In order to achieve the above object, this invention provides a controldevice for such an infinitely variable transmission for a vehicle thatcomprises an input shaft, a continuously variable transmission whichoutputs the rotation of the input shaft at an arbitrary speed ratio, afixed speed ratio transmission which outputs the rotation of the inputshaft at a fixed speed ratio, and an output shaft which changes arotation direction and a rotation speed according to a differencebetween an output rotation speed of the continuously variabletransmission and an output rotation speed of the fixed speed ratiotransmission.

The control device comprises a sensor which detects a running state ofthe vehicle, a sensor which detects a real vehicle acceleration, and aprogrammable controller that controls the speed ratio of thecontinuously variable transmission.

The controller is programmed to calculate a target speed ratio of thecontinuously variable transmission based on the running state of thevehicle, set a target vehicle acceleration based on the running state ofthe vehicle, calculate an acceleration deviation of the target vehicleacceleration from the real vehicle acceleration, determine if apredetermined creep torque control condition holds based on the runningstate of the vehicle, calculate a corrected target speed ratio, if thepredetermined condition holds, to cause the acceleration deviation todecrease, and

control the speed ratio of the continuously variable transmission basedon the corrected target speed ratio.

The controller may alternatively be programmed to calculate a targetspeed ratio of the continuously variable transmission based on therunning state of the vehicle, set a target vehicle acceleration based onthe running state of the vehicle, determine if a predetermined creeptorque control condition holds based on the running state of thevehicle, calculate a corrected target speed ratio, if the predeterminedcondition holds, to cause a ratio of the rotation speed of the inputshaft with respect to the rotation speed of the output shaft to becomesmaller as the target vehicle acceleration becomes larger, and controlthe speed ratio of the continuously variable transmission based on thecorrected target speed ratio.

This invention also provides a control method for the above describedinfinitely variable transmission. The control method comprises detectinga running state of the vehicle, detecting a real vehicle acceleration,calculating a target speed ratio of the continuously variabletransmission based on the running state of the vehicle, setting a targetvehicle acceleration based on the running state of the vehicle,calculating an acceleration deviation of the target vehicle accelerationfrom the real vehicle acceleration, determining if a predetermined creeptorque control condition holds based on the running state of thevehicle, calculating a corrected target speed ratio, if thepredetermined condition holds, to cause the acceleration deviation todecrease, and controlling the speed ratio of the continuously variabletransmission based on the corrected target speed ratio.

The details as well as other features and advantages of this inventionare set forth in the remainder of the specification and are shown in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an infinitely variable transmission(IVT) to which this invention is applied.

FIG. 2 is a schematic diagram of a speed ratio control device accordingto this invention.

FIG. 3 is a diagram showing the characteristics of a map of an IVT speedratio ii stored by a controller according to this invention.

FIG. 4 is a diagram showing a relation between a step number of a stepmotor and a CVT speed ratio ic.

FIG. 5 is a flowchart describing a main routine for speed ratio controlexecuted by the controller.

FIG. 6 is a flowchart describing a subroutine executed by the controllerfor calculating a real vehicle acceleration.

FIG. 7 is a flowchart explaining a subroutine executed by the controllerfor speed ratio control in a neutral range.

FIG. 8 is a flowchart describing a subroutine executed by the controllerfor change-over control from the neutral range to a forward travelrange.

FIG. 9 is a flowchart describing a subroutine for change-over controlfrom the forward travel range to the neutral range, executed by thecontroller.

FIG. 10 is a flowchart describing a subroutine executed by thecontroller for creep torque control in a forward travel range in a powerrecirculation mode.

FIG. 11 is a flowchart describing a subroutine executed by thecontroller for calculating a target input shaft rotation speed.

FIG. 12 is a diagram showing the characteristics of a speed ratio map inthe drive range stored by the controller.

FIG. 13 is a flowchart describing a subroutine executed by thecontroller for calculating a final target IVT speed ratio.

FIG. 14 is a flowchart describing a subroutine executed by thecontroller for calculating a transient target IVT speed ratio.

FIG. 15 is a flowchart describing a subroutine executed by thecontroller for calculating a target output torque of the IVT.

FIG. 16 is a diagram showing the characteristics of a map of targetoutput torque stored by the controller.

FIG. 17 is a flowchart describing a subroutine executed by thecontroller for calculating a CVT speed ratio feedback correction amountGFBRTO and an integral part GIntgR thereof according to the vehicleacceleration.

FIGS. 18A and 18B are diagrams showing the characteristics of a map of atorque shift compensation amount basic value CRPRTOM stored by thecontroller.

FIG. 19 is a flowchart describing a subroutine executed by thecontroller for normal speed ratio control in the forward travel range inthe power recirculation mode.

FIG. 20 is a flowchart describing a subroutine executed by thecontroller for calculating a command step number DSRSTP of the stepmotor.

FIG. 21 is a diagram showing the characteristics of a map specifying therelation between a target CVT speed ratio command value DSRRTO and atarget step number DSRSTP0 of the step motor.

FIG. 22 is a diagram showing the characteristics of a map of an oiltemperature correction amount CSTEP stored by the controller.

FIG. 23 is a diagram showing the characteristics of a map specifying arelation between a target oil pressure of a clutch and a duty ratio of asolenoid valve, stored by the controller.

FIGS. 24A-24M are timing charts showing an example of control by thespeed ratio control device.

FIG. 25 is similar to FIG. 10, but showing a second embodiment of thisinvention.

FIG. 26 is a diagram showing the characteristics of a map of a CVT speedratio open loop control amount GFFRTO stored by the controller.

FIG. 27 is similar to FIG. 20, but showing the second embodiment of thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, an infinitely variable transmission(referred to hereafter as IVT) comprises an input shaft 1 connected toan engine of a vehicle, a toroidal continuously variable transmission(referred to hereafter as CVT) 2, a reduction gear set 3 as a fixedspeed ratio transmission, a planetary gear set 5, and an output shaft 6.

The input shaft 1 is connected to an input gear 3A of the reduction gearset 3. A CVT input shaft 1B of the CVT 2 rotates together with the inputshaft 1 via a loading cam, not shown.

The CVT 2 comprises two sets of toroidal units comprising an input disk21 and output disk 22. A pair of power rollers 20 are gripped betweenthese facing input disk 21 and output disk 22. The rotation of the twooutput disks 22 is output from a sprocket 2A to a sprocket 4A supportedfree to rotate on the output shaft 6 arranged parallel to the CVT inputshaft 1B via a chain 4A.

The reduction gear set 3 is provided with an output gear 3B supportedfree to rotate on the output shaft 6. The output gear 3B meshes with theinput gear 3A, and the rotation of the input shaft 1 is output to theoutput gear 3B after reduction according to a gear ratio of the inputgear 3A and output gear 3B.

The planetary gear set 5 comprises a sun gear 5A, planet gears 5D, ringgear 5C and a planet carrier 5B which supports planet gears 5D. The sungear 5A is connected to the sprocket 4A via a sleeve-shaped hollow shaft4 supported on the circumference of the output shaft 6. The sprocket 4Ais also connected to the output shaft 6 via a direct clutch 10.

The planet gears 5D are plural pinions arranged between the sun gear 5Aand ring gear 5C, and are supported free to rotate and free to turnaround the sun gear 5A by the planet carrier 5B. The output gear 3B ofthe reduction gear set 3 and the planet carrier 5B are connected via apower recirculation clutch 9.

The ring gear 5C is connected to the output shaft 6.

A final output gear 7 is fixed to the output shaft 6. The rotation ofthe final output gear 7 is output to a vehicle drive shaft 11 via afinal gear 12 and differential 8.

The speed ratio ii of this IVT is expressed as the ratio of the rotationspeed INREV of the input shaft 1 and rotation speed OUTREV of the outputshaft 6. The speed ratio ic of the CVT 2 is expressed as the ratio ofthe rotation speeds of the input disk 21 and output disk 22. Therotation speed of the input disk 21 is equal to the rotation speed INREVof the input disk 1.

In the following description, the speed ratio ii of the IVT is referredto as IVT speed ratio and the speed ratio ic of the CVT 2 is referred toas CVT speed ratio.

Referring to FIG. 2, a rotation speed sensor 81 which detects therotation speed of the input gear 3A of the reduction gear set 3, and arotation speed sensor 82 which detects the rotation speed No of thesprocket 4A, are installed in the IVT. Here, the rotation speed of theinput gear 3A is equal to the rotation speed INREV of the input shaft 1and CVT input shaft 1B and it is also equal to the rotation speed Ne ofthe engine. The rotation speed No of the sprocket 4A is equal to therotation speed of the sun gear 5A. The rotation speed INREV and rotationspeed No respectively input as signals to a controller 80.

The controller 80 comprises one or a plurality of microcomputers each ofwhich is provided with a central processing unit (CPU), read-only memory(ROM), random access memory (RAM) and input/output interface (I/Ointerface).

The vehicle is provided with a brake pedal, accelerator pedal and arange selector lever.

A brake signal BRK from a brake switch 86 which detects whether or notthe brake pedal is depressed, a depression amount signal APS from anaccelerator pedal depression sensor 84 which detects a depression amountof the accelerator pedal, a selection range signal RNG from an inhibitorswitch 85 which detects a selection range of the selector lever, an idlesignal IDLE from a idle switch 87 which detects whether or not theengine is idling, and an oil temperature signal TEMP from an oiltemperature sensor 88 which detects an oil temperature in the CVT 2 arealso input to the controller 80. The selection range signal RNGdifferentiates between a low range (L), drive range (D), reverse range(R), neutral range (N) and park range (P).

Based on these signals, the controller 80 engages and releases the powerrecirculation clutch 9 via a solenoid valve 91 and the direct clutch 10via a solenoid valve 92. The speed ratio and transmission torque duringforward motion and reverse motion of the vehicle are also controlled byvarying the speed ratio ic of the CVT 2.

In a direct mode, wherein the power recirculation clutch 9 is releasedand the direct clutch 10 is engaged, the IVT outputs the output rotationof the toroidal CVT 2 to the final output shaft 6. On the other hand, ina power recirculation mode wherein the power recirculation clutch 9 isengaged and the direct clutch 10 is disengaged, the IT varies therotation direction and rotation speed of the output shaft 6 according tothe speed difference between the output rotation of the toroidal CVT 2and output rotation of the reduction gear set 3.

The controller 80 stores a map having the characteristics shown in FIG.3, and by referring to this map, applies the power recirculation modewhen the vehicle is reversing and when it is moving forward at a lowspeed where the IVT speed ratio ii is large, and applies the direct modewhen it is moving forward at is high speed where the IVT speed ratio iiis small. The change-over between these modes is performed at arevolution synchronization point (RSP) where the rotation of the outputshaft 6 is equal in both modes. In the power recirculation mode, therotation direction of the output shaft 6 is changed over at a gearedneutral point (GNP) where the output shaft 6 stops its rotation.

The CVT speed ratio ic varies according to the gyration angle of thepower rollers 20. The gyration angle of the power rollers 20 iscontrolled by a step motor 36. The controller 80 controls the speedratio ic of the CVT 2 by outputting a step number corresponding to atarget speed ratio to the step motor 36.

Referring to FIG. 4, the relation between the CVT speed ratio ic and thestep number input to the step motor 36 from the controller 80 will beexplained. In a toroidal CVT, when the input torque increases in apositive direction, the CVT speed ratio tends to increase, i.e., ittends to vary in the direction towards low gear, and when the inputtorque tends to decrease, i.e., it tends to vary in the directiontowards high gear. This phenomenon is known as a torque shift.

In the IVT, the direction of torque passing through the CVT 2 changesdepending on the drive mode. When in forward traveling in the powerrecirculation mode, torque is transmitted from the output disk 22 to theinput disk 21. Hereinafter, this torque transmitting direction will bereferred to as a negative direction. When the vehicle is travellingrearward or when it is travelling forward in the direct mode, torque istransmitted from the input disk 21 to the output disk 22. This torquetransmitting direction will be referred to as a positive direction.

In forward traveling in the power recirculation mode, as thetransmitting torque of the CVT 2 in the negative direction increases,the CVT speed ratio tends to decrease, as a result, the IVT speed ratiotends to increase. In order to compensate the torque shift and maintaina predetermined speed ratio, it is required to drive the step motor 36in a direction opposite to the direction of the variation of the CVTspeed ratio due to the torque shift.

Next, the speed ratio control of the IVT by the controller 80 will bedescribed.

The controller 80 refers first to a speed ratio map previously stored inthe memory and calculates a final target input shaft rotation speedDSRREV based on the accelerator pedal depression amount APS detected bythe accelerator pedal depression sensor 84 and the vehicle speed VSPdetected by the vehicle speed sensor 83.

Next, the controller 80 divides the final target input shaft rotationspeed DSRREV by the rotation speed OUTREV of the output shaft 6 that isdetected by the vehicle speed sensor 83 to calculate a final target IVTspeed ratio DIVTRATIO. The CVT speed ratio ic is controlled based onthis final target IVT speed ratio DIVTRATIO.

Further, the controller 80 changes over the drive mode by selectivelyengaging the power recirculation clutch 9 and direct clutch 10 at therevolution synchronization point RSP.

In the power recirculation mode, the controller 80 determines whether ornot the vehicle running condition is in the creep torque control regionbased on the vehicle speed VSP and accelerator pedal depression amountAPS.

When the vehicle running condition is in the creep torque controlregion, the controller 80 calculates a target vehicle accelerationTGTGDATA and control the CVT speed ratio based on the difference betweenthe target vehicle acceleration TGTGDATA and a real vehicle accelerationGDATA.

Referring to the flowcharts of FIGS. 5-11, FIGS. 13-15, FIG. 17 andFIGS. 19 and 20, the routines executed by the controller 80 for theabove control will be described.

The flowchart shown in FIG. 5 corresponds to a main routine of the speedratio control the controller 80 executes.

This routine is executed at periodic intervals of ten milliseconds whenthe range selector lever selects ranges other than park range (P). Allthe flowcharts except for FIG. 5 describe subroutines that are executeddepending on the execution of the main routine.

Referring to FIG. 5, in a step S1, the controller 80 reads the rotationspeed INREV of input shaft 1 and CVT input shaft 1B detected by therotation speed sensor 81, the rotation speed No of the sprocket 4Adetected by the rotation speed sensor 82, the vehicle speed VSP or therotation speed OUTREV of the output shaft 6 detected by the rotationspeed sensor 83, the selection range RNG of the range selector leverdetected by the inhibitor switch 85, and the brake signal BRK from thebrake switch 86.

In a next step S2, the controller 80 calculates the real vehicleacceleration GDATA by executing a subroutine shown in FIG. 6.

Referring to FIG. 6, in a first step S20, the controller 80 calculates adifference between the rotation speed OUTREV of the output shaft 6 and aprevious value OUTREV⁻¹ thereof that was detected on the immediatelypreceding occasion when the subroutine was executed. The real vehicleacceleration GDATA is then calculated by multiplying the difference by apredetermined constant KG.

In a next step, the controller 80 stores the rotation speed OUTREV ofthe output shaft 6 as the previous value OUTREV⁻¹ in the memory andterminates the subroutine.

Referring again to FIG. 5, after calculating the a real vehicleacceleration GDATA, the controller 80 calculates a real CVT speed ratioRATIO in a next step S3 by dividing the rotation speed INREV of the CVTinput shaft 1B by the rotation speed No of the sprocket 4A.

Steps S4 through S8 correspond to determination of a drive mode flagSFTMODE. The drive mode flag SFTMODE is set to any integer includingthose from zero to four by subroutines that will be described later.

In the step S4, it is determined if the drive mode flag SFTMODE has avalue of zero.

If the drive mode flag SFTMODE has a value of zero, a subroutine forspeed ratio control in the neutral range that is shown in FIG. 7 isexecuted in a step S9.

If the drive mode flag SFTMODE has a value other than zero, it isdetermined if the flag SFTMODE has a value of unity in the step S5.

If the drive mode flag SFTMODE has a value of unity, a subroutine forchange-over control from the neutral range to the forward travel rangethat is shown in FIG. 8 is executed in a step S10.

Herein, the forward travel range denotes any of the drive range (D) orthe low range (L) and may be abbreviated as (DL).

If the drive mode has a value other than unity in the step S5, it isdetermined in the step S6 if it has a value of two.

If the drive mode flag SFTMODE has a value of two, a subroutine forchange-over control from the forward travel range to the neutral rangethat is shown in FIG. 9 is executed in a step S11.

If the drive mode has a value other than two in the step S6, it isdetermined in the step S7 if it has a value of three.

If the drive mode has a value of three, a subroutine for creep torquecontrol in the forward travel range in the power recirculation mode thatis shown in FIG. 10 is executed in a step S12.

If the drive mode flag SFTMODE has a value other than three in the stepS7, it is determined in the step S8 if it has a value of four.

If the drive mode flag SFTMODE has a value of four, a subroutine fornormal control in the forward travel range in the power recirculationmode that is shown in FIG. 19 is executed in a step S13.

If the drive mode flag SFTMODE has a value other than four in the stepS8, a subroutine for the other ranges is executed in a step S14. Theother ranges include the drive range in the direct mode and the reverserange.

Although the subroutines applied in these two ranges are totallydifferent from each other, since the control in these two ranges havenothing to do with the subject matter of this invention, thesesubroutines are represented by the single step S14 and their descriptionis omitted.

With respect to the operation of the range selector lever, it should benoted that the ranges are arranged in a row in the order of park range(P), reverse range (R), neutral range (N), low range (L) and drive range(D). So, when the range selector lever is shifted from the park range(P) or reverse range (R) to the drive range (D), or vice versa, itnecessarily passes through the neutral range (N) in the course of itstravel. Therefore, the change-over routines between the neutral rangeand the forward travel range described above can also be applied tochange-over between the park or reverse range and the forward travelrange.

The drive mode flag SFTMODE determined in the steps S4 through S8 hasthe value that was set on the immediately preceding occasion when theroutine was executed.

If the drive mode flag SFTMODE is zero, for example, it means that therange selector lever was positioned in the neutral range (N) on theimmediately preceding occasion when the routine was executed.

The respective subroutines corresponding to the step S9 through the stepS14 calculate a command step number DSRSTP of the step motor 36, andparameters for determining duty signals DUTY1, DUTY2 of the solenoidvalves 91, 92.

Referring to FIG. 7, a subroutine for the speed ratio control in N rangewill be described. Herein, N range denotes the neutral range (N).

In a first step S40, it is determined if the present selection range RNGof the range selector lever is indicating the neutral range (N).

If the selection range RNG is indicating the neutral range (N), it meansthat the neutral range (N) continues from the immediately precedingoccasion when the routine was executed. In this case, the subroutineproceeds to a step S44.

If the selection range RNG is not indicating the neutral range (N), itmeans that the range selector lever has been shifted from the neutralrange (N) to one of the other ranges.

In this case, the subroutine proceeds to a step S41.

In the step S41, it is determined if the selection range RNG indicatesthe forward travel range (DL), i.e., the drive range (D) or the lowrange (L). When the selection range RNG is indicating the forward travelrange (DL), the controller 80 sets the drive mode flag SFTMODE topositive unity in a step S42 which is a value to command a N/DL rangechange-over control and terminates the subroutine.

When the selection range RNG is indicating neither the neutral travelrange (N) nor the forward travel range (DL), it denotes that theselection range is reverse range (R). In this case, the controller 80sets the drive mode flag SFTMODE to negative unity in a step S43 andterminates the subroutine.

In the step S44, a transient value INVIVTRATIO0 of an inverse of the IVTspeed ratio, a target pressure DSRPRSLC of the solenoid valve 91 forengaging the power recirculation clutch 9 and a target pressure DSRPRSHCof the solenoid valve 92 for engaging the direct connecting clutch 10are respectively set to zero. A transient target CVT speed ratio RATIO0is set equal to GNPRATIO. By this setting, in the neutral range (N), thepower recirculation clutch 9 as well as the direct connecting clutch 10are disengaged. GNPRATIO is a CVT speed ratio corresponding to thegeared neutral point GNP. When the transient value INVIVTRATIO0 of theinverse of the IVT speed ratio is zero, the transient target IVT speedratio is infinite.

In a next step S45, a torque shift compensation amount TSRTOMFL is resetto zero.

In a next step S46, a CVT speed ratio feedback control amount GFBRTObased on the vehicle acceleration and an integral part GIntgR thereofare respectively set to zero and the controller 80 terminates thesubroutine.

In the step S44 through the step S46, the reason that all the parametersother than RATIO0 are set to zero, is that, in the neutral range (N),the power recirculation clutch 9 as well as direct connecting clutch 10are disengaged and, since the CVT 2 does not transmit torque, the torqueshift compensation is not required.

Next, referring to FIG. 8, a subroutine for N/DL range change-overcontrol will be explained. The N/DL range change-over control denotesthe change-over control of the IVT from the neutral range (N) to theforward travel range (DL).

At first, in a step S50, the controller 80 determines if the presentselection range RNG of the range selector lever is indicating theneutral range (N).

If the selection range RNG is indicating the neutral range (N), it meansthat the range selector lever shifted again to the neutral range (N)after the last occasion of the subroutine execution, in which thechange-over to the forward travel range (DL) from the neutral range (N)was detected.

In this case, in a step S51, an increment INTGND in the hydraulicpressure supplied by the solenoid vale 91 and a timer value NDTIMER arerespectively reset to zero, and the drive mode flag SFTMODE is set totwo which is a value to command DL/N change-over. After the processingof the step S51, the controller 80 terminates the subroutine.

In the step S50, if the present selection range RNG of the selectorlever is not indicating the neutral range (N), the subroutine proceedsto a step S52.

In the step S52, the IVT speed ratio is maintained at the geared neutralpoint (GNP) by resetting the transient value INVIVTRATIO0 of the inverseof the IVT speed ratio to zero and setting the transient target CVTspeed ratio RATIO0 to the speed ratio GNPRATIO corresponding to thegeared neutral point.

In a next step S53, the torque shift compensation amount TSRTOMFL isreset to zero. This is because the CVT 2 does not transmit torque at thegeared neutral point (GNP).

In a step S54 through a step S64, the power recirculation clutch 9 whichhas been disengaged is brought into an engaged state.

At first, in the step S54, the timer value NDTIMER is compared with afirst predetermined value TND1. If the timer value NDTIMER is smallerthan the first predetermined value TND1, the subroutine proceeds to thestep S58. The initial value of the timer value NDTIMER is zero.Therefore, when the processing of the step S54 is executed for the firsttime, the timer value NDTIMER is necessarily zero, so the subroutineproceeds to the step S58 from the step S54.

In the step S58, the target pressure DSRPRSLC of the solenoid valve 91for engaging the power recirculation clutch 9 is set to the firstpre-charge pressure PND1.

When the processing of the step S58 is complete, the controller 80 addsunity to the timer value NDTIMER in the step S63, and terminates thesubroutine.

In the step S54, if the timer value NDTIMER is not smaller than thefirst predetermined value TND1, the subroutine proceeds to the step S55.Here, the timer value NDTIMER is compared with a second predeterminedvalue TND2. If the timer value NDTIMER is smaller than the secondpredetermined value TND2, the subroutine proceeds to the step S59.

In the step S59, the target pressure DSRPRSLC of the solenoid valve 91is set to a second pre-charge pressure PND2. The second pre-chargepressure PND2 is set to be a value which is larger than the firstpre-charge pressure PND1. After the processing of the step S59, thecontroller 80 adds unity to the timer value NDTIMER in the step S63, andterminates the subroutine.

In the step S55, if the timer value NDTIMER is not smaller than thesecond predetermined value TND2, the subroutine proceeds to the stepS56. Here, the timer value NDTIMER is compared with a thirdpredetermined value TND3. If the timer value NDTIMER is smaller than thethird predetermined value TND3, the subroutine proceeds to the step S60.

In the step S60, at first, increment INTGND in the hydraulic pressuresupplied by the solenoid valve 91 is calculated by the followingequation (1).

INTGND=INTGND ⁻¹ +DELTAGND   (1)

where,

INTGND⁻¹=the previous value of INTGND, the initial value of INTGND⁻¹being zero, and

DELTAGND=a constant.

In the next step S61, the target pressure DSRPRSLC of the solenoid valve91 is set to a value which is obtained by adding the increment INTGND tothe second pre-charge pressure PND2. Therefore, the target pressureDSRPRSLC increases on every occasion when the steps 60, 61 are executed.After the processing of the step 61 the controller 80 adds unity to thetimer value NDTIMER in the step S63 and terminates the subroutine.

In the step S56, if the timer value NDTIMER is not smaller than thethird predetermined value TND3, the subroutine proceeds to the step S57.Here, the timer value NDTIMER is compared with a fourth predeterminedvalue TND4. If the timer value NDTIMER is smaller than the fourthpredetermined value TND4, the subroutine proceeds to the step S62.

In the step S62, the target pressure DSRPRSLC of the solenoid valve 91is set to a maximum value which is a pressure when the powerrecirculation clutch 9 is fully engaged. After the processing of thestep S62, the controller 80 adds unity to the timer value NDTIMER in thestep S63, and terminates the subroutine.

In the step S57, if the timer value NDTIMER is not smaller than thefourth predetermined value TND4, the controller 80 resets the incrementINTGND and the timer value NDTIMER to zero and sets the drive mode flagSFTMODE to three which is a value to command creep torque control in thepower recirculation mode in the step S64, and terminates the subroutine.

The fourth predetermined value TND4 is larger than the thirdpredetermined value TND3, which is larger than the second predeterminedvalue TND2, which is larger than the first predetermined value TND1.

Thus, the subroutine expends a time period corresponding to the fourthpredetermined value TND4 in engaging the power recirculation clutch 9.

Next, referring to FIG. 9, a subroutine for DL/N change-over controlwill be explained. The DL/N change-over control denotes the change-overcontrol of the IVT from the forward travel range (DL) to the neutralrange (N).

At first, in a step S70, the controller 80 determines if the presentselection range RNG of the range selector lever is indicating theforward travel range (DL), i.e., the drive range (D) or the low range(L). When the selection range RNG is indicating the forward travel range(DL), it means that the range selector lever shifted again to theforward travel range (DL) after the last occasion of the subroutineexecution, in which the change-over to the neutral range (N) from theforward travel range (DL) was detected. In this case, in a step S71, theincrement INTGND in the hydraulic pressure supplied by the solenoidvalve 91 and the timer value DNTIMER are respectively reset to zero, thedrive mode flag SFTMODE is set to unity which is a value to command N/DLchange-over, and the controller 80 terminates the subroutine.

In the step S70, if the present selection range RNG of the rangeselector lever is not indicating the forward travel range (DL), thesubroutine proceeds to a step S72.

In the step S72, the transient value INVIVTRATIO0 of the inverse of theIVT speed ratio is reset to zero, the transient target CVT speed ratioRATIO0 is set equal to GNPRATIO corresponding to the geared neutralpoint, and the target pressure DSRPRSLC of the solenoid valve 91 for thepower recirculation clutch 9 is set to zero.

In a next step S73, the controller 80 resets the torque shiftcompensation amount TSRTOMFL to zero.

In a next step S74 through a step S80, the power recirculation clutch 9which has been engaged is brought into a disengaged state.

First in the step S74, a timer value DNTIMER is compared with the firstpredetermined value TDN1. If the timer value DNTIMER is smaller than theTDN1, the subroutine proceeds to the step S76. The initial value of thetimer value DNTIMER is zero. Therefore, when the processing of the stepS74 is executed for the first time, the timer value DNTIMER isnecessarily zero, so the subroutine proceeds to the step S76 from thestep S74.

In the step S76, at first, a decrement INTGDN in the hydraulic pressuresupplied by the solenoid valve 91 is calculated by the followingequation (2).

INTGDN=INTGDN ⁻¹ +DELTAGDN   (2)

where,

INTGDN⁻¹=the previous value of INTGDN, the initial value of INTGDN beingzero, and

DELTAGDN=a negative constant.

The decrement INTGDN is expressed as a negative value.

In the next step S77, the target pressure DSRPRSLC of the solenoid valve91 is set to a value which is obtained by adding the decrement INTGDN toa first predetermined value PDN1. As understood from the above equation,since the decrement INTGDN is a negative value, the target pressureDSRPRSLC decreases on every occasion when the steps S76, S77 areexecuted. After the processing of the step S76, the controller 80 addsunity to the timer value DNTIMER in the step S79, and terminates thesubroutine.

In the step S74, if the timer value DNTIMER is not smaller than thefirst determined value TDN1, the subroutine proceeds to the step S75.Here, the timer value DNTIMER is compared with a second predeterminedvalue TDN2. If the timer value DNTIMER is smaller than the secondpredetermined value TDN2, the subroutine proceeds to the step S78.

In the step S78, the target pressure DSRPRSLC of the solenoid valve 91is set to zero. After the processing of the step S78, the controller 80adds unity to the timer value DNTIMER in the step S79, and terminatesthe subroutine.

In the step S75, if the timer value DNTIMER is not smaller than thesecond predetermined value TDN2, the controller 80 resets the decrementINTGDN and the timer value DNTIMER to zero and sets the drive mode flagSFTMODE to zero which is a value to command the speed ratio control inthe Neutral range (N) in the step S80, and terminates the subroutine.

Next, referring to FIG. 10, a subroutine for creep torque control in theDL range in the power recirculation mode will be explained.

First, in a step S90, the controller 80 determines if the presentselection range RNG of the range selector lever is indicating theneutral range (N).

If the selection range RNG is indicating the neutral range (N), it meansthat the range selector lever shifted again to the neutral range (N)after the last occasion of the subroutine execution, in which thevehicle running condition was determined to be in the creep torquecontrol region. In this case, in a step S91, the controller 80 sets thedrive mode flag SFTMODE to two which is a value to command the DL/Nrange change-over control. After the processing of the step S91, thecontroller 80 terminates the subroutine.

In the step S90, when the selection range RNG of the selector lever isnot indicating the neutral range (N), the subroutine proceeds to a stepS92.

In the step S92, it is determined if the conditions that the acceleratorpedal depression amount APS is smaller than a predetermined value APS#1,and that the idle signal IDLE is ON, are both satisfied. If eithercondition is not satisfied, the controller 80 sets the drive mode flagSFTMODE to four which is a value to command the normal control in the DLrange in the power recirculation mode in a step S94, and terminates thesubroutine.

In the step S92, if the accelerator pedal depression amount APS issmaller than the predetermined amount APS#1 and the idle signal IDLE isON, the subroutine proceeds to a step S93. Here, the vehicle speed VSPis compared with a predetermined vehicle speed VSP#1. Herein, thepredetermined vehicle speed VSP#1 is set equal to five kilometers perhour (5 km/hr).

If the vehicle speed VSP is not smaller than the predetermined vehiclespeed VSP#1, in the step S94, the controller 80 sets the drive mode flagSFTMODE to four and terminates the subroutine as described above. On theother hand, if the vehicle speed VSP is smaller than the predeterminedvehicle speed VSP#1, the controller 80 executes the control of creeptorque in a step S95 through a step S107.

First, in the step S95, a subroutine shown in FIG. 11 is executed tocalculate a final target input shaft rotation speed DSRREV.

Referring to FIG. 11, the controller 80, first determines if theselection range RNG of the range selector lever is indicating the driverange (D) or the low range (L) in a step S110, and selects a mapaccording to the selection range from a plurality of speed ratio mapsprestored in the memory of the controller 8. The characteristics of themap for the drive range (d) is shown in FIG. 12.

In a next step S111, referring to the selected map, the controller 80obtains the target input shaft rotation speed DSRREV based on therotation speed OUTREV and the accelerator pedal depression amount APS.

Referring to FIG. 10 again, after calculating the target input shaftrotation speed DSRREV in the step S95, the controller 80 calculates aninverse INVDIVTRATIO of the final target IVT speed ratio by execution ofa subroutine shown in FIG. 13 in a step S96.

Referring to FIG. 13, this subroutine will be explained.

First in a step S115, the final target input shaft rotation speed DSRREVis divided by the rotation speed OUTREV of output shaft 6 to calculatethe final target IVT speed ratio DIVTRATIO.

In a next step S116, the inverse INVDIVTRATIO of the final target IVTspeed ratio DIVTRATIO is calculated.

Referring to FIG. 10 again, after calculating the inverse INVDIVTRATIOof the final target IVT speed ratio in the step S96, the controller 80calculates the transient value INVIVTRATIO0 of the inverse of thetransient target IVT speed ratio by execution of the subroutine shown inFIG. 14 in a next step S97.

Referring to FIG. 14, this subroutine will be explained.

First, in a step S120, the controller 80 calculates a time constant TgTMshowing characteristics of a change in speed ratio in a transient stateof IVT based on the accelerator pedal depression amount APS and vehiclespeed VSP.

In a next step S121, the controller calculates a transient target IVTspeed ratio IVTRATIO0 from the final target IVT speed ratio DIVTRATIOand the time constant TgTM by the following equation (3).

IVTRATIO0=IVTRATIO0 ⁻¹ +TgTM·(DIVTRATIO−IVTRATIO0⁻¹)  (3)

where,

IVTRATIO0 ⁻¹ the previous value of IVTRATIO0.

In a next step S122, the transient value INVIVTRATIO0 of the inverse ofthe transient target IVT speed ratio is calculated by the followingequation (4).

INVIVTRATIO0=INVIVTRATIO0 ⁻¹ +TgTM·(INVDIVTRATIO−INVIVTRATIO0 ⁻¹)  (4)

where,

INVIVTRATIO0 ⁻¹=the previous value of INVIVTRATIO0.

The equations (3) and (4) correspond to a general low pass filter with afirst order delay to set a target value in a transient state. It is alsopossible to replace the filter by that with the second order delaydepending on the purpose of IVT control.

Referring again to FIG. 10, after executing the above subroutine, in anext step S98, the controller 80 calculates the transient target CVTspeed ratio RATIO0 with reference to a map having the characteristicsshown in FIG. 3 based on the transient value INVIVTRATIO0 of the inverseof the transient target IVT speed ratio. The map is previously stored inthe memory of the controller 80. The transient target CVT speed ratioRATIO0 corresponds to a target speed ratio defined in the Claims.

In a next step S99, the controller 80 calculates a creep torque byexecuting a subroutine shown in FIG. 15.

Referring to FIG. 15, in a first step S125, the controller 80 obtains abasic value TGTTOM of IVT target output torque with reference to a maphaving the characteristics shown in FIG. 16 based on the rotation speedOUTREV of the output shaft 6 and the brake signal BRK. The map ispreviously stored in the memory of the controller 80.

According to this map, the basic value TGTTOM of IVT target outputtorque increases as the rotation speed OUTREV of the output shaft 6decreases. Specifically, when the brake switch 86 is OFF, the vehicleaccelerates by the output torque of IVT when it is larger than a torqueequivalent to the travel resistance. The torque equivalent to the travelresistance on a flat road is shown by a thin line in FIG. 15 and in therange where the output torque of IVT surpasses this line, the vehicleaccelerates. The basic value TGTTOM of IVT target output torque when thebrake switch is ON is always under this line regardless of the rotationspeed OUTREV of the output shaft 6.

It means that as long as the brake switch 86 is ON during traveling on aflat road, the IVT exerts torque in a decelerating direction on thevehicle.

In a next step S126, the controller 80 calculates an IVT target outputtorque TGTTO by the following equation (5) which also corresponds to alow pass filter.

TGTTO=TGTTO ⁻¹ +KTO·(TGTTOM−TGTTO ⁻¹)  (5)

where,

TGTTO⁻¹=the previous value of TGTTO, and

KTO=a time constant.

Due to the above processing, even when the brake is repeatedly operated,the IVT target outputting torque TGTTO is prevented from fluctuating.Therefore, this processing helps to stabilize the feedback control ofthe output torque of IVT.

Referring again to FIG. 10, after calculating the IVT target outputtorque TGTTO in the step S99, the controller 80 calculates the targetvehicle acceleration TGTGDATA in a next step S100 based on the IVTtarget output torque TGTTO by the following equation (6).

TGTGDATA=(TGTTO−TORL)·KCONV  (6)

where,

TORL=a travel resistance of the vehicle including energy loss due towind and resistance by gradient, and

KCONV=a conversion factor depending on vehicle weight, tire diameter,etc.

Next, in a step S101, the controller 80 compares the vehicle speed VSPwith a predetermined vehicle speed VSP#2. The predetermined vehiclespeed VSP#2 is set to a value between one kilometer per hour (1 km/hr)and two kilometers per hour (2 km/hr). If the vehicle speed VSP is notlarger than the predetermined vehicle speed VSP#2, the controller 80determines if the brake signal BRK is ON in a step S102. If the brakesignal BRK is ON, the controller 80 regards that the vehicle is at restand executes a process of a step S104.

Specifically, the transient value INVIVTRATIO0 of the inverse of thetransient target IVT speed ratio is reset to zero, the transient targetCVT speed ratio RATIO0 is reset to GNPRATIO corresponding to GNP.Further, a CVT speed ratio feedback correction amount GFBRTO and anintegral part GIntgR thereof are respectively reset to zero. After thisprocessing, the subroutine proceeds to a step S105.

On the other hand, if the real vehicle speed VSP is larger than thepredetermined vehicle speed VSP#2 in the step S101, or if the brakesignal BRK is OFF in the step S102, the vehicle is determined to betraveling by the creep torque. In this case, the controller 80calculates the CVT speed ratio feedback correction amount GFBRTO and theintegral part GIntgR thereof by executing the subroutine shown in FIG.17 in a step S103.

Referring to FIG. 17, in a first step S138, the controller calculates anacceleration deviation gerr from the real vehicle acceleration GDATAcalculated in the step S2 and the target vehicle acceleration TGTGDATAcalculated in the step S100 by the following equation (7).

gerr=TGTGDATA−GDATA  (7)

In a next step S139, the integral part GIntgR of the CVT speed ratiofeedback correction amount is calculated by the following equation (8),and the CVT speed ratio feedback correction amount GFBRTO based on theacceleration deviation gerr is calculated by the following equation (9)respectively.

GIntgR=GIntgR ⁻¹ +gerr·Kig  (8)

where,

GIntgR⁻¹=the previous value of GIntgR, and

Kig=an integral gain.

GFBRTO=gerr·Kpg+GIntgR  (9)

where,

Kpg=a proportional gain.

The equations (8) and (9) are known equations for proportional/integralcontrol (PI control). As can be understood from the equations, thegreater the acceleration deviation gerr, the larger the feedbackcorrection amount GFBRTO.

After calculating the CVT speed ratio feedback correction amount GFBRTOin the step S103 or S104 of the subroutine in FIG. 10, the controller 80executes the processing of a step S105.

In the step S105, the controller 80 calculates a torque shiftcompensation amount basic value CRPRTOM of CVT speed ratio during thecreep torque control with reference to a map having the characteristicsshown in FIG. 18A. This map is also previously stored in the memory ofthe controller 80. This map is a three dimensional map depending on thetarget output torque TGTTO and CVT speed ratio ic as parameters.

According to this map, the ratio of input torque and output torque ofthe CVT 2 is determined based on the CVT speed ratio ic. The control ofcreep torque is generally performed when the IVT speed ratio ii is inthe vicinity of the geared neutral point (GNP). In other words, thecontrol zone of creep torque is limited to the case where the CVT speedratio ic resides in the vicinity of the geared neutral point (GNP) inFIG. 3.

Since the CVT speed ratio ic during the creep torque control may beconsidered to have a fixed value, it is also possible to determine thetorque shift compensation amount basic value CRPRTOM with reference to amap which depends only on the target output torque TGTTO as shown inFIG. 18B instead of using the three dimensional map of FIG. 18A.

In a next step S106, the controller 80 calculates a torque shiftcompensation amount TSRTOMFL by the following equation (10) based on thetorque shift compensation amount basic value CRPRTOM.

TSRTOMFL=TSRTOMFL ⁻¹ +KTS·(CRPRTOM−TSRTOMFL ⁻¹)  (10)

where,

TSRTOMFL⁻¹=the previous value of TSRTOMFL, and

KTS=a time constant.

The equation (10) also corresponds to a low pass filter.

In a next step S107, the controller 80 sets the target pressure DSRPRSHCof the solenoid valve 92 to zero in order to disengage the directconnecting clutch 10, while setting the target pressure DSRPRSLC of thesolenoid valve 91 to a maximum value in order to connect the powerrecirculation mode clutch 9. After the processing of the step S107, thecontroller 80 terminates the subroutine.

By executing the subroutine of FIG. 10, the speed ratio ic of the CVT 2is determined depending on the speed ratio map of IVT, the feedbackcorrection amount based on the vehicle acceleration and the torque shiftcompensation amount. In actuality, a further correction, which isdescribed later, is applied to compensate the response delay of the stepmotor 36.

Next, referring to FIG. 19, a subroutine for the normal control of thespeed ratio in the DL range in the power recirculation mode will beexplained.

First in a step S150, the controller 80 determines if the followingthree conditions are simultaneously satisfied. The conditions are thatthe accelerator pedal depression amount APS is not greater than thevalue of (a predetermined amount APS#1-α), the idle signal IDLE is ON,and the vehicle speed VSP is not greater than the value of (apredetermined vehicle speed VSP#1-β. If all of these conditions aresatisfied, the subroutine proceeds to a step S151.

If these three conditions are satisfied, the controller 80 considersthat the creep torque control conditions are satisfied. In this case, inorder to execute the creep torque control in the next occasion when themain routine is executed, the controller 80 sets the drive mode flagSFTMODE equal to three in a step S151, which is the value to command thecreep torque control. Further, in a next step S152, the controller 80sets the CVT speed ratio feedback correction amount GFBRTO and theintegral part GIntgR thereof to be equal to zero. After the processingof the step S152, the subroutine is terminated.

The determination in the step S150 is performed in the opposite way tothe determination performed in the steps S92 and S93 of the subroutineof FIG. 10 for determining if the creep torque control conditions aresatisfied.

If on the other hand any of the three conditions is not satisfied in thestep 150, the controller 80 considers that the creep torque controlconditions are not satisfied. In this case, the subroutine proceeds to astep S153, and executes normal speed ratio control in the drive range(D) or low range (L). After the processing of the step S153, thesubroutine is terminated.

The normal speed ratio control is summarized as follows.

Referring to the map of FIG. 11, the final target input shaft rotationspeed DSRREV is determined from the vehicle speed VSP and acceleratorpedal depression amount APS. The final target IVT speed ratio DIVTRATIOis calculated from the final target input shaft rotation speed DSRREVand the vehicle speed VSP, and the transient target IVT speed ratioIVTRATIO0 is calculated based on the final target IVT speed ratioDIVTRATIO. Then, based on the transient target IVT speed ratioIVTRATIO0, the transient target CVT speed ratio RATIO0 is obtained fromthe map of FIG. 3. The step number corresponding to the transient targetCVT speed ratio RATIO0 is then output to the step motor 36. This normalspeed, ratio control process of IVT is known by U.S. Pat. No. 6,174,261.

In parallel with the speed ratio control, the hydraulic pressure of thesolenoid valves 91, 92 is controlled based on the real CVT speed ratioRATIO so as to selectively apply the power recirculation mode or thedirect mode.

Now referring again to FIG. 5, the rest of the main routine will bedescribed. After executing any of the processing of the step S9 throughthe step S14, the controller 80 calculates the command step numberDSRSTP of the step motor 36 by executing a subroutine shown in FIG. 20in a step S15.

Referring to FIG. 20, in a first step S180, the controller 80 calculatesa corrected transient target CVT speed ratio RATIO1 by adding the CVTspeed ratio feedback correction amount GFBRTO set in any of thesubroutines corresponding to the step S9 through the step S14, to thetransient target CVT speed ratio RATIO0 set in the same subroutine. Thecorrected transient target CVT speed ratio RATIO1 corresponds to acorrected target speed ratio defined in the Claims.

In a next step S181, a speed ratio deviation err is calculated from thecorrected transient target CVT speed ratio RATIO1 and the real CVT speedratio RATIO.

In a next step S182, a feedback correction amount FBRTO of CVT speedratio based on the speed ratio deviation err is calculated by applyingthe following equations (11) and (12).

IntgR=IntgR ⁻¹ +err·Ki  (11)

where,

IntgR=an integral part of the feedback correction amount,

IntgR⁻¹=the previous value of IntgR, and

Ki=an integral gain.

FBRTO=err·Kp+IntgR  (12)

where,

Kp=a proportional gain.

The equations (11) and (12) correspond to proportional/integral control(PI control).

In a next step S183, by using the corrected transient target CVT speedratio RATIO1, the feedback correction amount FBRTO of CVT speed ratiobased on the speed ratio deviation err, and the torque shiftcompensation amount TSRTOMFL, a target CVT speed ratio command valueDSRRTO is calculated by the following in equation (13).

DSRRTO=RATIO1+FBRTO+TSRTOMFL  (13)

In a next step S184, the controller 80 converts the target CVT speedratio command value DSRRTO to the step number of the step motor 36 withreference to a map having the characteristics shown in FIG. 21.

The map is previously stored in the memory of the controller 80. Thisstep number obtained in this way is referred to as a target step numberDSRSTP0.

In a next step S185, the controller 80 obtains an oil temperaturecorrection amount CSTEP based on the temperature TEMP that the oiltemperature sensor 88 has detected, with reference to a map having thecharacteristics shown in FIG. 22.

The map is previously stored in the memory of the controller 80. The oiltemperature correction amount CSTEP is a value to compensate the errorwhich appears in the relation between the operating position of the stepmotor 36 and the speed ratio of the CVT 2 depending on the oiltemperature in the CVT 2.

In a next step S186, a command step number DSRSTP is calculated byadding the oil temperature correction amount CSTEP to the target stepnumber DSRSTP0.

Referring again to FIG. 5, after calculating the command step numberDSRSTP in this way in the step S15, the controller 80 converts thetarget pressure DSRPRSLC and DSRPRSHC of the solenoid valves 91 and 92to the duty signals DUTY1 and DUTY2 for the solenoid valves 91 and 92 ina next step S16 with reference to a map having the characteristics shownin FIG. 23. The map is previously stored in the memory of the controller80. The target pressure DSRPRSLC and DSRPRSHC are values which were setin any of the subroutines corresponding to the steps S9 through thesteps S14.

In a last step S17, the controller 80 outputs the command step numberDSRSTP to the step motor 36, and outputs the duty signals DUTY1 andDUTY2 to the solenoid valves 91 and 92. After the processing of the stepS17, the controller 80 terminates the main routine.

Next, referring to FIGS. 24A-24M, the variation in creep torque underthe above creep torque control when the vehicle starts will bedescribed.

At a time T0, as shown in FIG. 24A, the range selector lever is in theneutral range (N), and the accelerator pedal is not depressed as shownin FIG. 24B. In this state, the controller 80 disengages both of thepower recirculation clutch 9 and direct connecting clutch 10 byexecuting the subroutine for N range in FIG. 7 in the step S9 of themain routine, and holds the CVT speed ratio of the CVT a to GNPRATIOcorresponding to the geared neutral point GNP as shown in FIG. 24I. Inthis state, the output torque of the output shaft 6 is zero as shown inFIG. 24M. The drive mode flag SFTMODE is set equal to zero as shown inFIG. 24D.

Although the brake pedal is depressed and the brake signal BRK turns ONbetween the time T0 and T1, however, this state continues regardless ofthe brake signal BRK as long as the drive mode flag SFTMODE has a valueof zero.

At the time T1, the driver shifts the range selector lever from theneutral range (N) to the drive range (D) as shown in FIG. 24A.

Accordingly, the controller 80 sets the drive mode flag to unity in thesubroutine of FIG. 7. The controller 80 detects the change of the drivemode flag SFTMODE to unity in the step S5 of the main routine in thenext occasion when the main routine is executed, and executes thesubroutine for N/DL range change-over of FIG. 8 in the step S10 of themain routine. In the subroutine of FIG. 8, the controller 80 engages thepower recirculation clutch 9 over the predetermined time TND4 as shownin FIG. 24E. The CVT speed ratio is still kept at GNPRATIO correspondingto the geared neutral point (GNP).

At a time T2, the power recirculation clutch 9 completely engages.

As a result, the drive mode flag SFTMODE is set to have a value of threein the step S64 of the subroutine for N/DL range change-over of FIG. 8.The controller 80 detects the change of the drive mode flag SFTMODE tothree in the step S7 of the main routine in the next occasion when themain routine is executed, and executes the subroutine of FIG. 10 for thecreep torque control in the DL range in the power recirculation mode inthe step S12 of the main routine.

Since the brake signal is still ON, the CVT speed ratio set in the stepS104 of FIG. 10 is still equal to GNPRATIO corresponding to the gearedneutral point (GNP) as shown in FIG. 24I. Therefore, as shown in FIG.24F, the command step number DSRSTP output to the step motor 36 has theGNP equivalent value. As the IVT speed ratio is kept at the gearedneutral point GNP until the time T3 when the brake signal BRK changes toOFF, the CVT 2 transmits no torque.

Therefore, as shown in FIGS. 24G and 24H, the torque shift compensationamount TSRTOMFL as well as the CVT speed ratio feedback correctionamount GFBRTO based on the acceleration deviation gerr are both zero.Further, as shown in FIG. 24J, the engine rotation speed Ne is held tothe idle rotation speed. As shown in FIGS. 24K and 24L, the vehiclespeed VSP as well as the vehicle acceleration GDATA are also zero. Thetorque output to the output shaft 6, i.e., the output torque of the IVTis also maintained at zero as shown in FIG. 24M.

When the brake signal BRK is changed to OFF at the time T3 the targetoutput torque TGTTO calculated in the step S99 of the subroutine of FIG.10 increases as shown in FIG. 24M. As a result, the target vehicleacceleration TGTGDATA calculated in the step S100 increases, and the CVTspeed ratio feedback correction amount GFBRTO calculated in the stepS139 of the subroutine of FIG. 17 also increases.

Hence, the target CVT speed ratio command value DSRRTO calculated in thestep S183 of the subroutine of FIG. 20 starts to increase from GNPRATIOas shown in FIG. 24F as soon as the brake signal BRK changes from ON toOFF, and IVT starts to transmit torque to the output shaft 6.

In the calculation of the step number of the step motor 36, the CVTspeed ratio feedback correction amount GFBRTO is added to the transienttarget CVT speed ratio RATIO0 to calculate the corrected transienttarget CVT speed ratio RATIO1. Further, the feedback correction amountFBRTO based on the speed ratio deviation err and the torque shiftcompensation amount TSRTOMFL are added to RATIO1 to calculate the targetCVT speed ration command value DSRRTO. As a result, the target CVT speedratio command value DSRRTO has a larger value than the transient targetCVT speed ratio RATIO0.

The output torque of the IVT is zero when the rotation speed OUTREV ofthe output shaft 6 is zero, i.e., the CVT speed ratio is equal toGNPRATIO, but when the CVT speed ratio slightly increases from GNPRATIO,it abruptly increases and then gradually decreases as the CVT speedratio increases further. These characteristics are apparent from the mapof FIG. 5.

Correcting the CVT speed ratio in the increasing direction when thevehicle starts to move at the time T3 as described above, realizessmooth vehicle acceleration and smooth increase in the output torque ofthe output shaft 6.

At a time T4, as shown in FIG. 24K, when the vehicle speed reaches thepredetermined value VSP#1, the controller 80 sets the drive mode flagSFTMODE to have a value of four in the step S94 of FIG. 10. Thisprocessing completes the creep torque control in the DL range in thepower recirculation mode.

On the next occasion when the main routine of FIG. 5 is executed, thenormal control subroutine in the DL range in the power recirculationmode of FIG. 19 is executed in the step S13.

The creep torque variation described above is an example when thevehicle starts. When on the other hand the driver depresses the brakepedal to decelerate the vehicle to stop, the target output torque TGTTOof the IVT calculated based on the map of FIG. 16A decreases to a valuesmaller than the travel resistance. Accordingly, the target accelerationTGTGDATA takes a negative value. Since the CVT speed ratio is feedbackcontrolled according to the acceleration deviation gerr in order toachieve the negative target acceleration TGTGDATA, the vehicledecelerates as intended by the driver.

Next, referring to FIGS. 25-27, a second embodiment of this inventionwill be described.

According to the first embodiment, the CVT speed ratio was feedbackcontrolled based on the acceleration deviation gerr of the targetvehicle acceleration TGTGDATA with respect to the real vehicleacceleration GDATA. In this embodiment, the CVT speed ratio is correctedby open loop control based on the target vehicle acceleration TGTGDATA.

FIG. 25 shows a subroutine according to this embodiment for controllingvehicle creep torque in the forward travel range (DL) in the powerrecirculation mode. This subroutine replaces the subroutine of FIG. 10of the first embodiment. The subroutine only differs from that of FIG.10 in that the step S103 of FIG. 10 for calculating the CVT speed ratiofeedback correction amount GFBRTO based on the acceleration deviationgerr is replaced by a step S 103A. The other steps are identical tothose of the subroutine of FIG. 10.

In the step S103A, the controller 80 calculates a CVT speed ratio openloop correction amount GFFRTO by referring to a map previously stored inthe memory of the controller 80. According to this map, the CVT speedratio open loop correction amount GFFRTO is larger as the target vehicleacceleration TGTGDATA is larger as shown in FIG. 26.

FIG. 27 shows a subroutine according to this embodiment for calculatingthe command step number DSRSTP of the step motor 36 that replaces thesubroutine of FIG. 20 of the first embodiment.

This subroutine only differs from that of FIG. 20 in that the step S180for calculating the corrected transient target CVT speed ratio RATIO1 byapplying the CVT speed ratio feedback correction amount GFBRTO isreplaced by a step 180A. The other steps are identical to those of thesubroutine of FIG. 20.

In the step S180A, the controller 80 calculates the corrected transienttarget CVT speed ratio RATIO1 by adding the CVT speed ratio open loopcorrection amount GFFRTO calculated in the step S103A to the transienttarget CVT speed ratio RATIO0. According also to this embodiment, thegenerated creep torque is always consistent with the driver's intention.

The contents of Tokugan 2001-66289 with a filing date of Mar. 9, 2001 inJapan, are hereby incorporated by reference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art, inlight of the above teachings.

For example, in the above embodiments, the accelerator pedal depressionamount APS is used as a parameter for processing of the steps S92, S111,S120 and S150, however, a throttle opening sensor may be used instead ofthe accelerator pedal depression sensor 84, and throttle opening TVO maybe used as a parameter instead of accelerator pedal depression amountAPS for these processings.

Instead of the brake operation being detected by the brake switch 86,the brake operating state of the vehicle may be determined by detectinghydraulic pressure which activates the brake system of the vehicle or bydetecting a depression amount of the brake pedal with which the vehicleis provided.

The embodiments of this invention in which an exclusive property orprivilege is claimed are defined as follows:

What is claimed is:
 1. A control device for an infinitely variabletransmission for a vehicle, the infinitely variable transmissioncomprising an input shaft, a continuously variable transmission whichoutputs the rotation of the input shaft at an arbitrary speed ratio, afixed speed ratio transmission which outputs the rotation of the inputshaft at a fixed speed ratio, and an output shaft which changes arotation direction and a rotation speed according to a differencebetween an output rotation speed of the continuously variabletransmission and an output rotation speed of the fixed speed ratiotransmission, the device comprising: a sensor which detects a runningstate of the vehicle; a sensor which detects a real vehicleacceleration; and a programmable controller programmed to: calculate atarget speed ratio of the continuously variable transmission based onthe running state of the vehicle; set a target vehicle accelerationbased on the running state of the vehicle; calculate an accelerationdeviation of the target vehicle acceleration from the real vehicleacceleration; determine if a predetermined creep torque controlcondition holds based on the running state of the vehicle; calculate acorrected target speed ratio, if the predetermined condition holds, tocause the acceleration deviation to decrease; and control the speedratio of the continuously variable transmission based on the correctedtarget speed ratio.
 2. The control device as defined in claim 1, whereinthe controller is further programmed to set a transient target speedratio of the infinitely variable transmission based on the runningstate, calculate a transient target speed ratio of the continuouslyvariable transmission from the transient target speed ratio of theinfinitely variable transmission, calculate a feedback correction amountbased on the deviation of the target vehicle acceleration and the realvehicle acceleration, and calculate the corrected target speed ratio byadding the feedback correction amount to the transient target speedratio of the continuously variable transmission.
 3. The control deviceas defined in claim 1, wherein the vehicle running state detectingsensor comprises a sensor which detects a depression state of anaccelerator pedal with which the vehicle is provided, and the controlleris further programmed to determine that the predetermined condition isnot established when the accelerator pedal is depressed.
 4. The controldevice as defined in claim 1, wherein the vehicle running statedetecting sensor comprises a sensor which detects a vehicle speed, andthe controller is further programmed to determine that the predeterminedcondition does not hold when the vehicle speed is greater than apredetermined vehicle speed.
 5. The control device as defined in claim1, wherein the vehicle running state detecting sensor comprises a sensorwhich detects an operation state of a brake with which the vehicle isprovided, and the controller is further programmed to set the targetvehicle acceleration when the brake is operating to a smaller value thanwhen the brake is not operating.
 6. The control device as defined inclaim 1, wherein the vehicle running state detecting sensor comprises asensor which detects a depression state of an accelerator pedal withwhich the vehicle is provided, and the controller is further programmedto set a target output torque of the output shaft according to thedepression state of the accelerator pedal and calculate the targetvehicle acceleration from the target output torque.
 7. The controldevice as defined in claim 6, wherein the vehicle running statedetecting sensor further comprises a sensor which detects an operationstate of a brake with which the vehicle is provided, and the controlleris further programmed to set the target output torque when the brake isoperating to a smaller value than when the brake is not operating. 8.The control device as defined in claim 6, wherein controller is furtherprogrammed to calculate a torque shift compensation amount based on thetarget output torque and control the speed ratio of the continuouslyvariable transmission to a sum of the corrected target speed ratio andthe torque shift compensation amount.
 9. The control device as definedin claim 1, wherein the vehicle running state detecting sensor comprisesa sensor which detects whether or not the vehicle is at rest, and thecontroller is further programmed to control the speed ratio of thecontinuously variable transmission to cause the rotation speed of theoutput shaft to become zero when the vehicle is at rest.
 10. The controldevice as defined in claim 1, wherein the real vehicle accelerationdetecting sensor comprises a sensor which detects a vehicle speed andthe controller programmed to calculate the real vehicle accelerationfrom a variation in the vehicle speed.
 11. A control device for aninfinitely variable transmission for a vehicle, the infinitely variabletransmission comprising an input shaft, a continuously variabletransmission which outputs the rotation of the input shaft at anarbitrary speed ratio, a fixed speed ratio transmission which outputsthe rotation of the input shaft at a fixed speed ratio, and an outputshaft which changes a rotation direction and a rotation speed accordingto a difference between an output rotation speed of the continuouslyvariable transmission and an output rotation speed of the fixed speedratio transmission, the device comprising: means for detecting a runningstate of the vehicle; means for detecting a real vehicle acceleration;and means for calculating a target speed ratio of the continuouslyvariable transmission based on the running state of the vehicle; meansfor setting a target vehicle acceleration based on the running state ofthe vehicle; means for calculating an acceleration deviation of thetarget vehicle acceleration from the real vehicle acceleration; meansfor determining if a predetermined creep torque control condition holdsbased on the running state of the vehicle; means for calculating acorrected target speed ratio, if the predetermined condition holds, tocause the acceleration deviation to decrease; and means for controllingthe speed ratio of the continuously variable transmission based on thecorrected target speed ratio.
 12. A control method for an infinitelyvariable transmission for a vehicle, the infinitely variabletransmission comprising an input shaft, a continuously variabletransmission which outputs the rotation of the input shaft at anarbitrary speed ratio, a fixed speed ratio transmission which outputsthe rotation of the input shaft at a fixed speed ratio, and an outputshaft which changes a rotation direction and a rotation speed accordingto a difference between an output rotation speed of the continuouslyvariable transmission and an output rotation speed of the fixed speedratio transmission, the method comprising: detecting a running state ofthe vehicle; detecting a real vehicle acceleration; calculating a targetspeed ratio of the continuously variable transmission based on therunning state of the vehicle; setting a target vehicle accelerationbased on the running state of the vehicle; calculating an accelerationdeviation of the target vehicle acceleration from the real vehicleacceleration; determining if a predetermined creep torque controlcondition holds based on the running state of the vehicle; calculating acorrected target speed ratio, if the predetermined condition holds, tocause the acceleration deviation to decrease; and controlling the speedratio of the continuously variable transmission based on the correctedtarget speed ratio.
 13. A control device for an infinitely variabletransmission for a vehicle, the infinitely variable transmissioncomprising an input shaft, a continuously variable transmission whichoutputs the rotation of the input shaft at an arbitrary speed ratio, afixed speed ratio transmission which outputs the rotation of the inputshaft at a fixed speed ratio, and an output shaft which changes arotation direction and a rotation speed according to a differencebetween an output rotation speed of the continuously variabletransmission and an output rotation speed of the fixed speed ratiotransmission, the device comprising: a sensor which detects a runningstate of the vehicle; a sensor which detects a real vehicleacceleration; and a programmable controller programmed to: calculate atarget speed ratio of the continuously variable transmission based onthe running state of the vehicle: set a target vehicle accelerationbased on the running state of the vehicle; determine if a predeterminedcreep torque control condition holds based on the running state of thevehicle; calculate a corrected target speed ratio, if the predeterminedcondition holds, to cause a ratio of the rotation speed of the inputshaft with respect to the rotation speed of the output shaft to becomesmaller as the target vehicle acceleration becomes larger; and controlthe speed ratio of the continuously variable transmission based on thecorrected target speed ratio.